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Where does reflected light go

enad
Prodigy 40 points

If I use NIR(1550nm) source with Light Commander, I will loose around 20% of it from front window of DMD for only one transmission through the window, see http://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/94/t/85503.aspx,  which is reflected from front window. Can anybody explain that where does this reflected light from the frond window of DMD go? it goes back to the source or some other directions. Can you a little bit elaborate this reflected light from front window in terms of directions it goes?

 

Second question is that if I buy only DMD and Controller Board of Light Commander (they are available separately from Light commander) do I need any extra hardware and software set up to be able to pattern mirrors? Can I use software developed for LC if I only buy DMD and Controller Board?

 

Thank you

  • 0
    TI__Guru 54510 points

    Hello Enad,

    This reflected energy will go to the walls of the housing by the output lens.  These walls are coated with a flat black to absorb such reflections and reduce stray reflections in the core module light path.

    I hope this helps.

     

    Fizix

  • 0 in reply to Fizix
    Prodigy 40 points

    Thank you for your reply,

    Since I am not familier with the device I mentioned, LC, I did not understand well your answer saying "housing" and "output lens". It sounds that this reflected energy goes output with spatially modulated light from mirrors, right? Could you be a little bit clear. Suppose I have a DMD device and I send light on it, and there is no other optics, lens. Since DMD has reflected window it reflects some energy. I just would like to know how much of this reflected light directly goes back to the source path (reflects back) and how much of it tracks the same path with modulated light from mirrors. In both cases this reflected light couses noise over the light from the sample and over modulated light going on sample. 

     

    Thank you

  • 0 in reply to enad
    TI__Guru 54510 points

    Enad,

    For a DMD usually the input illumination is 24 degrees from the normal of the window so that the specular reflection is at -24 degrees.  This is so that when the mirrors (12 degree tilt) are pointed toward the incoming light the rays will exit the DMD normal to the array (& window)  This means the specular reflection from the window and the "on" state light are separated by 24 degrees.   This is the most common configuration.

    If you illuminate the DMD normal to the array then the specular reflection will return to the source along the normal (law of reflection relected angle = - incident angle).  However now the "on" state will be exiting the DMD 24 degrees from the normal.  So the "on" state and the specular reflection will always be separated by 24 degrees.  This illumination is not used as often since it makes the optics more complicated on the output path.

     

    Fizix